Mongol conquest of the Song dynasty

The Mongol conquest of the Song dynasty occurred from 1235 to 1279 when the Mongol Yuan armies of Ogedei Khan and Kublai Khan gradually conquered the Song dynasty of southern China. In 1273, the Mongols captured the stronghold of Xiangyang, leaving the rest of China vulnerable to attack. In 1279, the last remnants of the Song were defeated at the naval Battle of Yamen, allowing for the Yuan to unite the country under Mongol rule.

Early efforts
In 1234, the Mongol Empire conquered the Great Jin dynasty of northern China with the help of the Song in the south. However, the Mongols soon turned their attention to conquering southern China, and their first territorial gain was Chengdu in 1241. When Mongke Khan became the new Great Khan in 1251, the Mongols renewed their offensive in China, conquering the Kingdom of Dali in Yunnan in 1253 and pacifying Yunnan and Tibet shortly after. In 1259, Mongke Khan was mortally wounded by cannon fire at Diaoyucheng, causing another halt in hostilities. After a civil war against Ariq Boke, Kublai Khan became the new Great Khan and sought to transform the Mongol Empire into the Yuan dynasty. In 1271, Kublai Khan proclaimed himself Emperor of China. Kublai Khan built 20,000 public schools, was a patron of the arts, adopted Buddhism, supported contact with foreigners, created a highly centralized government, and brought in gunpowder from his foreign allies. Kublai Khan came to rely on an army of mixed Mongol and Song composition, and he then set out to conquer the Song.

Kublai's conquest
The Song lacked strong armies but instead boasted some of the strongest fortresses in the world, chief among them Xiangyang. Kublai Khan built 5,000 ships (manned by Chinese sailors) and took the rivers of China, blocking enemy supplies. He then besieged Xiangyang, which went on for six years, as it held the most valuable position in China. Multiple Song breakout and relief attempts failed, and the Mongols' new counterweight trebuchet made the difference in storming Xiangyang, which fell in 1273. Kublai's forces quickly swept through southern China, and the Song sent emissaries to negotiate peace, but they were rejected. The Song ultimately assembled a huge fleet, and, on 19 March 1279, the massive Song fleet met Kublai Khan's fleet at the Battle of Yamen. The two fleets met on the Yinyu River, and the Song fleet chained its ships together, turning a naval battle into a land battle fought at sea. The Mongol ships attacked from the front and rear, firing arrows at the hapless Song sailors and massacring them. The Mongols suffered heavy losses and temporarily withdrew, only to launch a surprise attack on the Song fleet. As the Song fleet was destroyed, an important retainer of Emperor Bing of Song grabbed the child emperor and hurled himself into the sea, killing both of them in a defiant act of suicide. The Yuan became the first foreign dynasty to unite all of China, having destroyed the last remnants of the Song.